With the development of RFID (Radio Frequency Identification), RFID could not only be attached on the items as the electronic tags, but could also be used as a tool for information exchange. For example, in the school, RFID can be used as the interactive tools between the teachers and the students. The teachers send RF (radio frequency) signal which contains the questions to the students by a reader, the students receive the said signal by RFID, and then the students send the RF signal which contains the answers to the teachers' readers by RFID. Hence, the information exchanges between the teachers and the students achieve.
In the above-mentioned applications, a reader needs to exchange information with many RFIDs. However, when a large number of RFIDs send the RF signal to the reader at the same time, the reader could only receive a certain number of RF signal sent by RFID, and as a result that it is very easy to cause the signal collision which further reduce the speed of the reader to read the RF signal sent by the RFIDs and further reduce the reliability of the information exchange between the readers and RFIDs. Therefore, the existing RFID can only be used in the occasion with a few people participate in, but can not meet the need of the wider scope. And the current RFID usually adopts the non-working microwave band (below 2.45 GHz) passive RFID, so the reading scope of RF signal which can be reliably received by the reader from RFID is limited, which limits the applications of RFID.
In view of the above-mentioned shortcomings of existing technology, it is necessary to provide an improved technology to overcome the said shortcomings.